The present invention relates to a flexible electrical heat element made of insulated electrical feeder conductors and one or several heating conductors surrounding the insulated feeder conductors, whereby local baring a feeder conductor (not being a heat conductor) permits directly or through contact bridges contact making as between the heading element and the feeder conductor under formation of well defined heating zones. Specifically the wires or conductors may be arranged in juxtaposed positions or they may be stranded or bundled or otherwise combined whereby the heating conductors may in some form surround the electrical conductors either helically or through braiding, weaving, meandering or the like.
Heating elements of the type to which the invention pertains and following basically the outlined above or disclosed German printed patent application Nos. 32 33 904, 32 33 928 and 32 43 061 corresponding to U.S. Pat. No. 4,523,086 and Canadian Pat. No. 1,215,556. Heating elements of this combination and composite configuration can be cut into any kind of length. It is further customary to include a particular conductor which provides for measuring and/or monitoring function or other control operation or for feeding electrical current to farther points if the conductor as used is a rather long one.
The known heating elements for example can be wound upon a tubular conductor with relatively small pitch so that heat distribution on the surface of the tube as compared with other known heating elements with parallel running conductors is considerably improved. However, it can happen that following stronger bending e.g. including bending over small radii and following further restretching of the element assembly the contact between any feeder line and a heating conductor can be interrupted. This may be specifically the case if the heating conductor is made of Cr-Ni base material. Such a material is relatively stiff including particularly detrimental stiffness in the area of contact beween heating and regular conductors. Therefore, on strong bending there may occur physical separation.
In order to remedy the situation of contact disengagement it is known to provide the conductors in the area of the contact making with additional means e.g. soldering or other physical bonding and connection between the electrical feeder conductor and the heating conductor. This is specifically disclosed in German printed patent application No. 23 20 420. The contact between the feeder lines for the heating element pertaining to the cable and the heating conductor proper will in fact be maintained even in case of sever bending. However, it was found that no matter how one approaches this problem and its solution, the additional physical connection when made is a very expensive and significant part of manufacturing cost and, therefore interferes, with an economic continuous production. In addition certain problems obtain if the contact finds different kinds of material to be in direct contact such as the conductors of the feeder lines, the heating conductor and the solder being, third an interposing material.